Herbicides have been widely employed to destroy unwanted plants or "weeds", to prevent their growth on bare ground or in established crops, and to promote the growth of desirable plants, such as grains, fruits and vegetables. In fact, millions of pounds of herbicide are applied directly to the soil on an annual basis. In general, herbicides consist of two types, non-selective and selective. Non-selective herbicides kill all plant life on the plot of soil on which they are applied. Selective herbicides, on the other hand, kill or inhibit the establishment of certain types of plant life, such as weeds, while leaving the desirable, surrounding crops on which they are applied relatively undamaged. Examples of selective herbicides include phenolics, carbamates, and dinitroanilines.
One way to selectively eliminate unwanted plants without injuring surrounding plant life is to inhibit germination or establishment of the seeds of the unwanted plants. In order to accomplish this, a herbicide must be applied before the unwanted plants emerge from the soil, either to a bare plot of soil into which established plants will be transplanted, or to a plot of soil comprising an established stand of desirable plants, but relatively few weeds. Such herbicides are often referred to as preemergence herbicides.
While various types of herbicides exist, most of them are based on synthetic chemical toxins. As a result of their toxic nature, they are undesirable for many applications. This is particularly a problem when these materials come in contact with the public as is the case in turfgrass areas and in the production of food crops consumed by humans. While synthetic chemical herbicides may effectively destroy unwanted plant life, they may contaminate the soil and the crops themselves. They may also contaminate the ground water as a result of run off or erosion.
The disadvantages of synthetic chemical herbicides have become more visible as a result of heightened public awareness and concern for environmental protection and consumer safety. This in turn has led to the search for non-toxic, natural herbicides which can provide a greater margin of safety for the public and for the environment. In the area of herbicides or insecticides, however, few effective materials derived from naturally-occurring sources are known. Bacillus thurigiensis (Bt toxins), Bacillus popilliae, Serratia eritomophila, Puccinia chondrillina, and Sclerotinia sclerotiotum represent some examples of natural herbicides and insecticides that currently exist.
Corn gluten meal is capable of inhibiting root growth of germinating plants, while no damage is observed to plants that have formed a mature root system. Christians (U.S. Pat. No. 5,030,268) discloses that this material is useful as a natural preemergence herbicide for various plant production systems, including turfgrass areas, where it acts to inhibit the establishment of annual weeds, such as crabgrass (Digitaria spp.).
Corn gluten meal, however, is essentially water-insoluble. This characteristic limits its use as an herbicide for some applications. Since corn gluten meal is insoluble and cannot be dissolved and sprayed, it is difficult to apply evenly. As a result, there is a risk that the soil on which it is applied will not be completely covered, thereby significantly reducing its effectiveness. Also, sprayable herbicides are advantageous for application to certain crops.
The effectiveness of a herbicide also depends upon its ability to permeate the soil. Water-insoluble or slightly soluble materials do not permeate the soil as well as do water-soluble materials. Factors such as wind or drought can further reduce the availability of such materials.
Therefore, a continuing need exists for potent, natural preemergence herbicides which are also highly water dispersible and/or water soluble.